Terpolymers for electron beam positive resists

ABSTRACT

Electron beam positive resists are formed from terpolymers of (a) an alpha olefin, (b) sulfur dioxide, and (c) a compound selected from the group consisting of cyclopentene, bicycloheptene and methyl methacrylate. The terpolymers have the particular unexpected advantage of being resistant to cracking of the films.

1.11m States atent 1 1 [111 3,898,350

Gi stein et al. Au 5, 1975 [54] TERPOLYMERS FOR ELECTRON BEAM 3,585,l l86/1971 Harada et al. 117/9331 P SIT VE RESIST 0 I S OTHER PUBLICATIONS[75] Inventors: Edward Gipstein; William Ainslie Hewett, both fsal-dtogaa C lif Brown et al., Macromolecules, Vol. 5, No. 2,March-April, 1972, pp. 109-114. [73] Ass1gnee: International BusinessMachines Corporation, Armonk, NY. Primary Examiner-J. I-l. NewsomeFlledl J 1974 Attorney, Agent, or Firm-Joseph G. Walsh 21 Appl. No.:483,589

[57] ABSTRACT [52] US. Cl. 427/43; 96/35.l; 96/362;

204/1592} 260/7931 A; 427/273 Electron beam posltwe reslsts are formedfrom ter- 51 11m.c1. B05D 3/06 Polymers of (a) an alpha Olefin (b)Sulfur dimdde [58] Field of Search 117/9331 8' 427/43 44- and (C) acompound Selected from the group 96/35 I 36 2 l 704/159 760/793 ing ofcyclopentene, bicycloheptene and methyl methh acrylate. The terpolymershave the particular unex- {561 References Cited pected advantage ofbeing resistant to cracking of the fl UNITED STATES PATENTS ms 3,535.13?10/1970 Haller et ul. l17/93.31 7 Claims, No Drawings TERPOLYMERS FORELECTRON BEAM POSITIVE RESISTS FIELD OF THE INVENTION The presentinvention is eoncernedwith a process for preparing electron beampositive resists. By the use of certain specified terpolymers there areobtained resists which are particularly resistant to cracking andcrazing of the films.

PRIOR ART Positive acting polymeric electron beam resists are well knownin the prior art. Such prior art is thoroughly discussed in, forexample, US. Pat. No. 3,535,137 of Haller et al. That patent provides avery good discussion of typical methods for fabricating and using resistmaterials. As is explained in that patent, the process typically startsby dissolving a suitable polymer in a solvent. A thin polymer film isthen formed on a substrate by a process such as, for example, spinning adrop of the dissolved polymer on the substrate surface and allowing itto dry. The polymer film may then be baked to improve the adhesion andhandling characteristics of the film. The next step involves exposingselected portions of the polymer film to electron beam radiation, in therange of 5 to 30 kilovolts. This radiation causes scission of the bondsof the polymer. As a result of such scissions, the portions of thepolymer film which have been exposed to the radiation may be selectivelyremoved by application of a developer solvent while leaving theunexposed portion of the film still adhered tothe substrate. When it isso desired, the remaining polymer film may be baked to eliminateundercutting. Following this, in cases where it is so desired, theexposed underlying substrate may be etched with a suitable etchant.

Typical solvents and developers suitable for use in the presentinvention include aromatic solvents such as m-xylene, chlorinatedsolvents such as carbon tetrachloride, esters such as methyl acetate,ethers such as tetrahydrofuran, ketones such as methyl isobutyl ketone,and hydrocarbons such as cyclopentane. Mixtures of solvents are alsouseful, with the optimum one depending upon the particular polymer beingused.

Prior art materials which have been particularly successful as positiveacting electron beam resists include poly (methyl methacrylate) andcertain poly (olefin sulfones). There are, however, relatively fewmaterials which simultaneously possess all of the required properties toact as resists. It is necessary that the material be chemicallyresistant to etching solutions but still degrade under electronradiation. The material must be capable of adhering to the substrate asa film, and the film must resist cracking. In particular, poly (olefinsulfones) have in the past been found to give brittle films. It has beenobserved that films of, for example, poly (cyclopentcne sulfone) or poly(bicycloheptene sulfone) when spun to a thickness greater than 3,000 Acraze or crack. In the past, various methods of attempting to improvethe film forming properties have been unsuccessfully tried. For example,when low molecular weight sulfones were added as plasticizers, thesematerials caused the films to become cloudy after spinning or else theyprecipitated out during the prebake step. When low molecular weightpolymer fractions were used, cracking was diminished but the electronsensitivity was reduced.

SUMMARY OF THE INVENTION It has now been found that crack and crazeresistant films suitable for use in positive acting electron beamprocesses may be prepared by the use of certain terpolymers. As far aswe are aware, the present application represents the first use ofterpolymers in electron beam resist technology.

The terpolymers suitable for use in the present invention are thoseformed from (a) alpha olefin, (b) sulfur dioxide, and (e) a compoundselected from the group consisting of cyclopentene, bicycloheptene andmethyl methacrylate. When these terpolymers are used as electron beamresists, sensitive but toughly adherent and crack resistant films areobtained.

The following Examples are given solely for the purpose of illustrationand are not to be deemed limitations of the present invention manyvariations of which are possible without departing from the spirit orscope thereof.

EXAMPLE 1 Synthesis of Polysulfone Terpolymers When two olefins can eachcopolymerize with S0 in a 1:1 ratio, the three component system alsobehaves as a 1:1 ratio (total vinyl monomerszso Poly( cyclopentenesulfone-eo-hexe'nel -sulfone) A mixture of 13.6 g (0.2 mole)cyclopentene, 33.6 g (0.3 mole) hexene-l and 0.36 g (4X1 0 mole) t-BHPO(t-butyl hydro peroxide) initiatordissolvec'l in 250 ml dry toluene waspolymerized at 20C with 48 g of S0 (0.75 mole) added dropwise to thestirred solution. After I hr. the viscous solution was poured into 2liters of cold MeOI-I to precipitate a white polymer. The polymer waspurified by dissolution in CHCl and reprecipitation in MeOI-I. Afterdrying 48 hr. at 45 under vacuum 56.7 g of product was obtained.

The terpolymer was characterized by several analytical methods:

1. Elemental Analysis for +C,,H S O Theory for Terpolymer Found- C 47.1247.13, @711 H 719 7.37, 7.20 S 22.87 23.08, -22.85 O 22.82 22.65, 22.85

2. Gel Permeation Chromatography (GPC) A monomodal distribution curvewas obtained of the polymer in CHCL, solvent from which the followingmolecular weight averages (compared to polystyrene standards) werecalculated by a computer programmed analysis.

mer but with about twice as much weight loss in the first step as thecopolymer (decomposition began at 102C). TMA measurements indicated thatthe T.. had

EXAMPLES 3-17 The tcrpolysulfones listed in Tables 1 and 11 wereprepared by the techniques described in the previous two Examples. Tablel contains terpolymcrs of eyclopen- O 20 n I o I been lowered to 59 ofPCPS lg 98 tene sulfone and Table 11 contains blcycloheptenesulhexene-l-polysulfone 15 -58 fone ter 01 mers The ter 01 mers re aredin Table 5. The NMR spectrum also indicated that the reactants p y p y pp I 111 were block polymers of methyl methacrylatc, olefin had combinedin a 1:1:2 ratlo (olefinszsO o and S0 Thesepolymers were prepared in asealed The terpolymer was heated 3 hr. at 100 C 1n vacuum parr reactorby heating the monomers at least 24 hr. at

to lose 2.6% of its orlglnal welght wlth a small change 50 i 2 C with afree radlcal 1n1tlator. The polymers in the molecular weight: M 330,425,M 159,942,

m /m 2 were purlfied by repeated preclpltatlon from chloroform solventinto methyl alcohol or petroleum ether, a Exposure of the terpolymer to3 Mrads of gamma radiation reduced the molecular weight: non'solvcm'Polycyclopentene sulfone films greater than 4000 A were observed tocrack during the prebake step or durm m Mir/m" ing development.Cyclopentene/butene-l-SO films 63,113 30.643 4000 to 9100 A thick didnot crack or craze and could be successfully processed to give excellentimages after The so1ub111ty of the terpolymer was enhanced over exposureFor example, 000 to 9000 A thick fil that of the individual copolymersso that films could be were spun f 7 10% solutions f the polymer in pfrom larger number of Solvents CH NO on $10 wafers precoated with BSA(bis mmeth lsil lacetamide ,an adhesion romoter, was re- EXAMPLE 2 bakedfor 1 hr. at 100 C under vacu lm. A pattern :vas Blcycloheptenesulfone'co'hexene' l 411K006) 7 written with an E-beam at 1 10 N sec.exposure 4XlO' A mixture of g 111016) y spts l cou1/cm and imagesdeveloped with a solvent mixture 8 m hexane-land g t-BHPO mmafor ofcycloheptanone and cyclohexanone (80/20). The

sob/Ed 350 ml cyclohexanone was Polymenzed at developed wafer waspost-baked at 165200C for 20 C Wlth. 2 48 g mole)- The P y was minutesto 1 hr. and then etched with HF for 5 minutes.

recovered from MeOH and gurlfied from 30 Excellent images of highdefinition and fidelity with CHCl3/MeOH. to give 48 g (78.3%) w itepolymer. fi line geometry remaine Elemental Anal sis for C H 80 y 1:1 222 4+" TABLEI Poly(Cyc1opentg1e Sulfone Terpo1 'mers Theory for Ill/2Terpolymer Found Example Olefin Mir Mn mw/M" Tr g 222 3 Hexene-l 339.200171.650 1.98. 6468C 5 2093 4 4 Butene-l 3.161.222 243,481 12.9 74C 5Cis-2- O 2038 2044 2038 Butene 408.800 109.600 3.72 70C 6 Trans-2- 40Butene 653.146 108.687 5.98 85C 7 Cis-trans- The GPC curve wasmonomodal: 1T1 90,879, l\ /l,, z'Butene 27mm) 88900 78C Pyrolysis gaschromatography combined with mass TABLE U spectrometry confirmed theterpolymer structure.

TMA measurements gave a T o1 6468C which is polymicydohepmw: sulfone)Terpolymers lower than the T.. of 8388C obtained for the PBCHS ExampleOlefin M M 1H,, T,.

Co 01 mer.

1 0] mer films 5 un from 710% 1 S-dichloro entane 8 Hexenc'l 91900 31600(448C P P 9 Octadecene-l 680.100 52.000 13.1 80C solutions gaveexfcellent crack-free films on S10 sub- 10 Ethylene 145.700 28.750 5.0374-82%.

l1 Cis-2-Butene 444.270 174.540 2.55 65 135C Ztggges. The adheslon ofthese films to the substrate was I 2 Butelw 194.416 59312 313 TABLE 111Methyl Methacrylate/Olefin/SO Block Terpolymers Exam 1e Monomers, GM.Catalyst. GM. Conversion. 7: Structure. Male '4 M... M,, M.,/M,.

P l3 MMA. 10.1 AlBN. 0.3 37 (MMA) 42 119K 45K 2.61

gtyreng. 10.4 gtoyrene) O 4 psig 1 14 MMA. 9.4 AlBN. 0.06 33 (Mb lA) 88116K 51K 2.27

llsxciise-l. 6.7 zgloexene-l) Z Si 2) l5 MMA. 10 AlBN. 0.07 65 (Mh/illA) 42 229K 40K 5.63

BCH. 9.5 (BC 29 SO 45psig (S02) 29 16 MMA. 9.4 AlBN. 0.07 14 (MMA) 98268K 107K .50

Butene-2(C.T).9.8 (sB(1;tene-,2)v 1 S02. 45 psig 17 MMA. 9.4 AlBN. 0.07(MMA) B 50 805K 42.5K 1.89

Butene-l. 5.6 (Butene-l 25 (S02) 25 S0 45psig From 5.0 Analyses What isclaimed is: I

1. A process for forming an electron beam positive resist comprising thesteps of forming on a substrate a terpolymcr film of (a) from l to 48mole '7: of an alpha olefin, (b) from 1 to 50 mole 7c of sulfur dioxide,and (c) from to 98 mole 7c of a compound selected from the groupconsisting of cyclopentene, bicyclohcptene and methyl methacrylatc, andexposing said film in a predetermined pattern to low energy electronbeam radiation.

2, A process as claimed in claim 1 wherein the exposure is continueduntil the exposed portion of the film has been rendered soluble in afluid which is not a solvent for the unexposed portion of the film.

3. A process as claimed in claim 1 wherein the elecmethyl methacrylate.

1. A PROCESS FOR FORMING AN ELECTRON BEAM POSITIVE RESIST COMPISING THESTEPS OF FORMING ON A SUBSTRATE A TERPOLYMER FILM OF (A) FROM 1 TO 48MOLE % OF AN ALPHA OLEFIN, (B) FROM 1 TO 50 MOLE % OF SULFUR DIOXIDE,AND (C) FROM 25 TO 98 MOLE % OF A COMPOUND SELECTED FROM THE GROUPCONSISTING OF CYCLOPENETENE, BICYCLOHEPTENE AND METHYL METHACRYLATE, ANDEPOSING SAID FILM IN A PREDETERMINED PATTERN TO LOW ENERGY ELECTRON BEAMRADIATION.
 2. A process as claimed in claim 1 wherein the exposure iscontinued until the exposed portion of the film has been renderedsoluble in a fluid which is not a solvent for the unexposed portion ofthe film.
 3. A process as claimed in claim 1 wherein the electron beamradiation is at an energy of from about 10 to about 30 KeV.
 4. A processas claimed in claim 1 wherein the exposed position of the film isremoved by a solvent.
 5. A process as claimed in claim 1 wherein theterpolymer is formed from hexene-1, sulfur dioxide and bicycloheptene.6. A process as claimed in claim 1 wherein the terpolymer is formed fromhexene-1, sulfur dioxide and cyclopentene.
 7. A process as claimed inclaim 1 wherein the terpolymer is formed from hexene-1, sulfur dioxideand methyl methacrylate.